Allergy patients are being warned of a potential fault with Emerade adrenaline pens.
The Medicines and Healthcare products Regulatory Agency (MHRA) said some have blocked needles, so cannot deliver adrenaline.
Around two in every 1,000 pens are thought to be affected.
Patients are advised to follow the existing advice to carry two pens at all times. Charities said it was a “very difficult” time for patients.
The fault was first found in routine testing by the pens’ makers, Bausch & Lomb, in June 2018, but it was believed to be extremely rare, affecting 1.5 per 10,000 pens.
Further testing led the company to now estimate that the fault affects 2.3 pens per 1,000.
But the MHRA says that if patients follow the advice to carry two pens at all times, the